Image forming apparatus

ABSTRACT

In a scanning optical system provided with a plurality of scanning optical devices, each scanning optical device including a light source to emit a light beam, a collimator lens into which the light beam emitted from the light source enters, a deflector to deflect the light beam passing through the collimator lens in a main scanning direction, an image forming lens to focus the light beam coming from the deflector onto a scanned surface, and a base plate on which the light source, the collimator lens, the deflector and the image forming lens are fixed, the plurality of scanning optical devices are piled up in a sub-scanning direction perpendicular to the main scanning direction in such a manner that each base plate is substantially parallel to other base plates; and the scanning optical system is further provide with a plurality of link members to connect two neighboring base plates independently of other base plates.

BACKGROUND OF THE INVENTION

[0001] This invention relates to an scanning optical device comprisingat least a light source, a collimator lens into which a light beamemitted from said light source enters, a deflector which deflects thelight beam having passed said collimator lens to the direction of mainscanning, and an image forming lens which focuses the light beam havingpassed said deflector on the surface to be scanned and to an imageforming apparatus having a plurality of the above-mentioned scanningoptical devices arranged in the direction of sub-scanning.

[0002] Generally speaking, in an image forming apparatus capable offorming a multi-color image, a cylinder-shaped, or belt-shaped imagebearing member is used. In forming a multi-color image by using thisimage bearing member, charging, exposure, and development are carriedout for each of colors with the image bearing member rotated (moved),and the multiple color toner images are superposed one after another onthe image bearing member and transferred onto a sheet of transfer paperby a one-time transfer operation.

[0003] Incidentally, in order to accomplish a high-speed printing, it isrequired not a structure such that exposure processing (writing bylight) for one color is carried out in every rotation of the imagebearing member but a structure such that the exposures for all of fourcolors Y, M, C, and K are carried out in every rotation of the imagebearing member. In this case, not only a plurality of the developingunits but also a plurality of the scanning optical devices correspondingto the respective colors should be provided in order that the multipleexposures and developments should be done at different positions on theimage bearing member.

[0004] For example, in the case where a color image is formed using thefour colors Y (yellow), M (magenta), C (cyan), and K (black), thescanning optical devices and the developing units for the respectivecolors Y, M, C, and K are arranged in the direction of sub-scanning, andeach of the scanning optical devices is let to form the latentelectrostatic image of the color corresponding to it in such a manner asto form the toner images precisely superposed on one another, and thelatent electrostatic images are developed.

[0005] In this case, to remark one pixel of the latent images formed bythe respective scanning optical devices, if the position of this pixelis deviated for a certain color, synthesis of the color can not be doneat this pixel portion, producing a color deviation and loweringresolution, and image quality is deteriorated. In order to prevent theoccurrence of this color deviation and the lowering of resolution, it isrequired that not only the characteristics of the respective scanningoptical devices are made to be the same so as to be able to write thesame scan line, but also the respective optical devices are fixed in aprecise positional relationship so as to make the scan lines for therespective colors coincide with one another.

[0006] To consider the characteristics of the scanning optical device asan individual one, it is desirable for obtaining a good image that thescan lines on the surface to be scanned are straight and, at the sametime, the arrangement of the pixels forming any one of the scan lineshas a uniform interval between any adjacent pixels. However, actually,the positioning of optical parts etc can not be precisely performed,therefore, there have been problems that scan lines on the surface to bescanned are curved and that the arrangement of the pixels forming a scanline has an uneven interval between pixels.

[0007] Further, in the case where a multi-color image is formed, therehas been a problem that the characteristics of the respective scanningoptical devices can not be made equal, neither the respective scanningoptical devices can be fixed in a precise positional relationship,resulting in deterioration of image quality.

SUMMARY OF THE INVENTION

[0008] This invention has been made in order to solve theabove-described problems, and it is an object of this inventionconcerning a scanning optical device to actualize a scanning opticaldevice capable of adjusting the scanning beam easily.

[0009] Further, it is an object of this invention concerning an imageforming apparatus to actualize an image forming apparatus capable ofgetting rid of the deterioration of image quality owing to the scanningoptical device.

[0010] The above object can be attained by the following structures.

[0011] A scanning optical system, comprises:

[0012] a plurality of scanning optical devices, each scanning opticaldevice including

[0013] a light source to emit a light beam,

[0014] a collimator lens into which the light beam emitted from thelight source enters,

[0015] a deflector to deflect the light beam passing through thecollimator lens in a main scanning direction,

[0016] an image forming lens to focus the light beam coming from thedeflector onto a scanned surface, and

[0017] a base plate on which the light source, the collimator lens, thedeflector and the image forming lens are fixed, wherein the plurality ofscanning optical devices are piled up in a sub-scanning directionperpendicular to the main scanning direction in such a manner that eachbase plate is substantially parallel to other base plates; and

[0018] a plurality of link members to connect two neighboring baseplates independently of other base plates.

[0019] A scanning optical system, comprises:

[0020] a plurality of scanning optical devices, each scanning opticaldevice including

[0021] a light source to emit a light beam,

[0022] a collimator lens into which the light beam emitted from thelight source enters,

[0023] a deflector to deflect the light beam passing through thecollimator lens in a main scanning direction,

[0024] an image forming lens to focus the light beam coming from thedeflector onto a scanned surface,

[0025] a contact member to come in contact with a first side surface ofthe image forming lens at three contact points on both end portions anda middle portion of the first side surface in terms of the main scanningdirection;

[0026] a pressing member to come in pressure contact with a second sidesurface of the image forming lens so as to press the image forming lenstoward the contact member and

[0027] a base plate on which the light source, the collimator lens, thedeflector, the image forming lens, the contact member and the pressingmember are fixed, wherein the plurality of scanning optical devices arepiled up in a sub-scanning direction perpendicular to the main scanningdirection in such a manner that each base plate is substantiallyparallel to other base plates; and

[0028] a plurality of link members to connect two neighboring baseplates independently of other base plates.

[0029] A scanning optical device, comprises:

[0030] a light source to emit a light beam;

[0031] a collimator lens into which the light beam emitted from thelight source enters;

[0032] a deflector to deflect the light beam passing through thecollimator lens in a main scanning direction;

[0033] an image forming lens to focus the light beam coming from thedeflector onto a scanned surface;

[0034] a contact member to come in contact with a first side surface ofthe image forming lens at three contact points on both end portions anda middle portion of the first side surface in terms of the main scanningdirection; and

[0035] a pressing member to come in pressure contact with a second sidesurface of the image forming lens so as to press the image forming lenstoward the contact member.

[0036] Further, the above object can be attained by the followingpreferable structures.

[0037] This invention concerning a scanning optical device is the onecomprising at least a light source, a collimator lens into which a lightbeam emitted from said light source enters, a deflector which deflectsthe light beam having passed said collimator lens to the direction ofmain scanning, and an image forming lens which focuses the light beamhaving passed said deflector on the surface to be scanned, said scanningoptical device further comprising contact members capable of being incontact with said image forming lens at three points, that is, the bothend portions of said image forming lens in the direction of mainscanning and an intermediate point between the both end pointsrespectively at the time of adjusting the position of said image forminglens, and an urging means for urging said image forming lens toward saidcontact members.

[0038] In this invention, a mechanism for adjusting and determining theposition of the image forming lens is provided. The image forming lensis positioned in the vicinity of the surface to be scanned, and is easyto have a bend owing to its long size. In spite of this, according tothis invention for adjusting the position to fix this image forminglens, the scanning beam is corrected easily and with a good efficiency.In addition to it, because the image forming lens is in contact with thecontact members at the three points, namely, the both end portions inthe main scanning direction and an intermediate portion between the bothend portions at the time of adjusting the position of the image forminglens, it is possible to let the image forming lens take any position bydisplacing the points of contact.

[0039] In this case, if the points of contact of the image forming lensat its both end portions in the main scanning direction with the contactmembers are made to be positioned on a straight line which isapproximately parallel to the main scanning direction, and the point ofcontact at the intermediate portion is placed at a position deviatedfrom a position on the above-mentioned straight line in the directionperpendicular to the surface to be scanned, the adjustment of positionof the image forming lens can be performed by moving at least one of thecontact members placed at the above-mentioned three points of contact inthe direction of sub-scanning.

[0040] It is desirable that the image forming lens is fixed to the basein order to prevent the deviation of the position of the image forminglens, after the adjustment and determination of the position of theimage forming lens. By carrying out this fixing at a position in theneighborhood of the point of contact at the intermediate portion of theimage forming lens, the image forming lens is fixed only at theintermediate portion, which makes it possible for the image forming lensto expand and contract freely in accordance with the variation oftemperature and humidity of the surrounding; thus the image forming lensis never bent unnaturally and it can be avoided the unfavorableinfluence that a complex bending etc are produced in the scan lines.

[0041] This invention concerning an image forming apparatus is the onehaving a plurality of scanning optical devices arranged in the directionof sub-scanning, each of said scanning optical devices comprising atleast a light source, a collimator lens into which a light beam emittedfrom said light source enters, a deflector which deflects the light beamhaving passed said collimator lens to the direction of main scanning,and an image forming lens which focuses the light beam having passedsaid deflector on the surface to be scanned, wherein any pair of theneighboring scanning optical devices are linked to each other, and thelinking between these scanning optical devices is made by fixing a linkmember to each of the scanning optical devices in a manner capable oftaking off, the position of one of the neighboring scanning opticaldevices being determined in the state of being freely movable(hereinafter referred to as ‘state of floating off’) against the other,and after that, fixing said linking members of the neighboring scanningoptical devices to one another.

[0042] According to this invention, the positions of a plurality ofscanning optical devices arranged in the direction of sub-scanning areadjusted and determined in the state of floating off against the others,and the linking members are mutually linked after determining thepositions. Owing to this, by once precisely adjusting and determiningthe positions of the respective scanning optical devices, the positionalrelationship among the scanning optical devices will never be variedafter that, and the deterioration of image quality owing to the scanningoptical device can be prevented.

[0043] Further, because the linking members are fixed to the respectivescanning optical devices in a manner capable of being taken off, in thecase where the determination of the positions is proved to be notsatisfactory after the linking of the neighboring scanning opticaldevices, it is possible that these link members are taken off from thescanning optical devices, with the state of mutual linking of the linkmembers let to remain as it is, and then a new link members are attachedto the scanning optical devices, and the positions are determined again,and the new link members are fixed to one another. Owing to this, it hasbecome possible to utilize again the scanning optical devices.

[0044] Another invention concerning an image forming apparatus is theone having a plurality of scanning optical devices arranged in thedirection of sub-scanning, each of said scanning optical devicescomprising at least a light source, a collimator lens into which a lightbeam emitted from said light source enters, a deflector which deflectsthe light beam having passed said collimator lens to the direction ofmain scanning, and an image forming lens which focuses the light beamhaving passed said deflector on the surface to be scanned, wherein eachof said scanning optical devices comprises contact members capable ofbeing in contact with said image forming lens at three points, that is,the both end portions of said image forming lens in the direction ofmain scanning and an intermediate point between the both end pointsrespectively at the time of adjusting the position of said image forminglens, and an urging means for urging said image forming lens toward saidcontact member, and further, any pair of the neighboring scanningoptical device are linked to each other, and the linking between thesescanning optical device is made by fixing a link member to each of thescanning optical devices in a manner capable of taking off, the positionof one of the neighboring scanning optical devices being determined inthe state of floating off against the other, and after that, fixing saidlinking members of the neighboring scanning optical devices to oneanother.

[0045] According to this invention, in each of the scanning opticaldevices, the scanning beam can be corrected easily and with a goodefficiency. Further, because the linking members are mutually linkedafter determining the positions, the positional relationship among thescanning optical devices is never varied, and the deterioration of imagequality owing to the scanning optical device can be prevented.Furthermore, reutilization of the scanning optical device has becomepossible.

[0046] If an adhesive of the UV-hardening type is used for theabove-described fixing of the scanning optical devices to one another,the determination of the positions is carried out with the adhesiveinjected into every clearance between the linking members, and thefixing can be done by applying an ultraviolet ray immediately after thedetermining of the positions, which makes the linking operation easy.

BRIEF DESCRIPTION OF THE DRAWINGS

[0047]FIG. 1 is the plan showing an example of the embodiment of thisinvention concerning a scanning optical device;

[0048]FIG. 2 is the front view showing the example of the embodiment ofthis invention concerning a scanning optical device;

[0049]FIG. 3 is the bottom view showing the example of the embodiment ofthis invention concerning a scanning optical device;

[0050]FIG. 4 is the enlarged plan showing a part of the base;

[0051]FIG. 5 is the front view of the second cylindrical lens;

[0052]FIG. 6 is the plan of the second cylindrical lens;

[0053]FIG. 7 is a cross-sectional view along the cutting line A-A inFIG. 5;

[0054]FIG. 8 is a perspective view showing the structure for urging thesecond cylindrical lens;

[0055]FIG. 9 is a drawing showing the structure of the scanning opticaldevice in the linked state;

[0056]FIG. 10 is a perspective view showing the structure of fitting alink member; and

[0057]FIG. 11 is a drawing showing the structure of the scanning opticaldevices in the linked state.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT THE FIRST EXAMPLE OFTHE EMBODIMENT

[0058]FIG. 1 to FIG. 3 are drawings for illustrating an example of theembodiment of this invention concerning a scanning optical device; FIG.1 is the plan, FIG. 2 is the front view, and FIG. 3 is the bottom view.

[0059] As shown in FIG. 1, the laser light source 2 emitting a laserbeam in the horizontal direction, the collimator lens 3, and the firstcylindrical lens 3′ are attached to the standing wall portion 11, and onthe bottom plate portion 12 of the base 1, there is provided thepolygonal mirror 4 as a deflector for deflecting the laser beam havingbeen emitted from the laser light source 2 and having passed thecollimator lens 3 in the direction of main scanning in such a manner asto be capable of rotating around a vertical axis. Further, on the bottomplate portion 12 of the base 1, there are attached the fθ lens 5 intowhich the laser beam reflected by the polygonal mirror 4 enters, and thesecond cylindrical lens 6 as an image forming lens for focusing thelaser beam having passed the fθ lens 5 on the surface to be scanned.

[0060] As shown in FIG. 4, at the mounting portion of the fθ lens 5 onthe bottom plate portion 12 of the base 1, there are provided theprojections 13 and 14 which are in contact with the lower surface of theboth end portions of the fθ lens 5, the projection 15 which is incontact with the lower surface of the intermediate portion of the fθlens 5, the projections 16 and 17 which are in contact with the sidesurface of the both end portions of the fθ lens 5, and the projection 18for adhesive bonding which faces the lower surface of the intermediateportion of the fθ lens 5. The fθ lens 5 is bonded by an adhesive to theprojection 18 for adhesive bonding after it is set in the state ofcontact with the above-mentioned projections 13 to 17.

[0061] As shown in FIG. 5 to FIG. 7, the second cylindrical lens 6 hasthe rim portion 61 at its upper portion and the rim 62 at its lowerportion, and the portion between them is the effective lens portion 63.At the lower surface of the both end portions of the rim portion 62, thesupporting portions 65 and 66 are formed respectively, and also at thelower surface of the intermediate portion of the rim portion 62, thesupporting portion 67 is formed. Further, the engaging projection 68 isformed on the supporting portion 67.

[0062] As shown in FIG. 1 and FIG. 4, at the mounting portion of thesecond cylindrical lens 6 on the bottom plate portion 12 of the base 1,there are provided the projections 19 and 20 which are capable of beingin contact with the lower surface of the supporting portions 65 and 66of the second cylindrical lens 6, the projections 22 and 23 which arecapable of being in contact with the side surface of the both endportions of the second cylindrical lens 6, and the projections foradhesive bonding 24 and 25 which face the lower surface of thesupporting portion 67 of the second cylindrical lens 6.

[0063] Further, at the positions in the neighborhood of the projections19 to 21 facing the supporting portions 65 to 67 respectively, the screwholes 26 to 28 are bored. Further, in the neighborhood of theprojections 22 and 23, the supporting rods 29 and 30 are fitted asprojected.

[0064] For mounting the second cylindrical lens 6 to the bottom plateportion 12 of the base 1, first, the second cylindrical lens 6 is placedon the projections 19 to 21 with the supporting portions 65 to 67positioned at the bottom. At this time, the side surfaces of the bothend portions of the cylindrical lens 6 are supported by the projections22 and 23, and the engaging projection 68 of the second cylindrical lens6 is fitted into the slot 24 a (refer to FIG. 4) of the projection foradhesive bonding 24 on the bottom plate portion 12. By this fit, thesecond cylindrical lens 6 is regulated with regard to the movement inthe main scanning direction.

[0065] Next, as shown in FIG. 1 and FIG. 8, the base portions of theleaf springs 31 and 32 as urging means are fixed to the supporting rods29 and 30 respectively by the screws 33 and 34, and the upper surfacesof the both end portions of the rim portion 61 of the cylindrical lens 6is pressed downward by the free end portions of the leaf springs 31 and32 (that is, the half-sphere-shaped projections 31 a and 32 a providedas projected downward in FIG. 8). This state of pressing is a temporaryfixed state by an elastic force, and if a force is exerted to the secondcylindrical lens 6, it can be removed.

[0066] In this example of the embodiment, for the purpose of performingthe adjustment of the position of the second cylindrical lens 6, thescrews for adjustment 36 to 38 as members for contact are forced to beinserted into the screw holes 26 to 28 from the bottom side. The frontends of these screws for adjustment 36 to 38 are capable of being incontact with the supporting portions 65 to 67 of the second cylindricallens 6 at least at the time of adjusting the position of the secondcylindrical lens 6, and if the front ends of the screws for adjustment36 to 38 are projected upward farther than the projections 19 to 21,they become in contact with the supporting portions 65 to 67 of thesecond cylindrical lens 6. Because the second cylindrical lens 6 isalways pressed by the half-sphere-shaped projections 31 a and 32 a ofthe leaf springs 31 and 32 toward the screws for adjustment 36 to 38, itis moved as engaged with the screws for adjustment 36 to 38.

[0067] In this example of the embodiment, the points of contact of thesecond cylindrical lens 6 against the screws for adjustment 36 and 37 atthe both end portions in the main scanning direction are positioned on astraight line which is approximately parallel to the main scanningdirection, and the point of contact at the intermediate portion againstthe screw for adjustment 38 is deviated from a position on theabove-mentioned straight line in the direction perpendicular to thesurface to be scanned.

[0068] Accordingly, by rotating the screws for adjustment 36 to 38separately to adjust the amount of projection, it is possible not onlythe parallel movement of the second cylindrical lens 6 in the upward anddownward direction (the direction of sub-scanning), but also its tiltingmovement in the upward and downward direction (rotation around an axisparallel to the direction of main scanning) or its tilting movement inthe left and right direction (rotation around an axis perpendicular tothe surface to be scanned); thus, the second cylindrical lens 6 can takeany desirable position. After this adjustment and determination of theposition for the second cylindrical lens 6, the rim portion 62 is bondedto the projections for adhesive bonding 24 and 25 by using an adhesiveof the UV-setting type or the like.

[0069] As shown in FIG. 2, in the front wall portion 40 of the base 1,which is positioned in front of the second cylindrical lens 6 and facesthe surface to be scanned, it is bored the slit 41 for letting the laserbeam having passed the second cylindrical lens 6 emerge, and the frame42 is formed in such a manner as to surround this slit 41. Further, inthis frame 42, the transparent cover 43 is bonded in such a manner as toclose the slit 41.

[0070] In the neighborhood of one end portion of the second cylindricallens 6, the mirror 7 is disposed in order that the laser beam havingentered on it from the polygonal mirror 4 through the fθ lens 5 may bereflected toward the photo-sensor 8 which is attached to the standingwall portion 11. This photo-sensor 8 is provided for detecting that thelaser beam reaches the predetermined beam position, and its output isused for the synchronization of main scanning.

[0071] The scanning by the laser beam in this example of the embodimentis quite the same as in the apparatus of the prior art. That is, thelaser beam having been emitted from the laser light source 2 to thehorizontal direction is made to be a parallel pencil of light by thecollimator lens 3, and after being regulated by a slit, which is notshown in the drawings, it enters onto the polygonal mirror 4; then, thereflected laser beam by the polygonal mirror 4 passes the fθ lens 5, andenters into the second cylindrical lens 6. Further, the laser beamhaving passed the second cylindrical lens 6 reaches the surface to bescanned through the slit 41.

[0072] In the above, because the polygonal mirror 4 is rotating, thebeam spot on the surface to be scanned moves to the direction of mainscanning, and an exposure process in accordance with the modulation inthe laser light source 2 is carried out. Further, because the surface tobe scanned is moving in the direction of sub-scanning, the surface to bescanned is exposed to the laser beam two-dimensionally. The exposurestart timing on every scanning line is determined on the basis of thephoto-sensor 8.

[0073] In this example of the embodiment, a mechanism for adjusting anddetermining the position of the second cylindrical lens 6 is provided.The reason for it is that the second cylindrical lens 6 is positionedclose to the surface to be scanned, and is easy to produce bendingbecause it is a long-sized lens. According to this example of theembodiment wherein the mounting position of the second cylindrical lens6 is adjusted, the scanning beam is corrected easily and in a goodefficiency. In addition to it, because the second cylindrical lens 6 isin contact with the contact members 37 to 39 at three points, that is,the both end portions in the main scanning direction and theintermediate portion between these both end points respectively at thetime of adjusting and determining the position of the second cylindricallens 6, it is possible to let the second cylindrical lens 6 take anyposition by displacing the contact points.

[0074] Further, after adjusting and determining the position of thesecond cylindrical lens 6, it is fixed to the base 1 in order to preventthe positional deviation of the second cylindrical lens 6; this fixingis done, in this example of the embodiment, in the neighborhood of thecontact point at the intermediate portion of the second cylindrical lens6. Owing to this, the second cylindrical lens 6 is fixed only at theintermediate portion, it can freely expand and contract in accordancewith the surrounding temperature and humidity, it is never bentunnaturally, and it can be avoided the unfavorable influence that acomplex bending etc are produced in the scan lines.

[0075] It will be explained in more detail the operation of adjustingand determining the position of the second cylindrical lens 6 in theabove-described example of the embodiment. In addition, here, theexplanation will be given on the condition that there is no tilt angleerror for each of the reflecting surfaces of the polygonal mirror 4.

[0076] The operation of adjusting and determining the position iscarried out for the scanning optical devices in the state wherein thesecond cylindrical lens 6 is temporarily fixed. At this time, for thescan line detecting portion of the fixture for adjustment, it is usedthe one wherein three sensors are arranged on an ideal scan line whichis assumed to be on the surface to be scanned. This sensor is the onecapable of detecting to what degree an actual beam is deviated from theabove-mentioned ideal scan line, and any method of detection can beused.

[0077] It can be known what kind of a curve an actual scan line istracing from the output of the three sensors when a laser beam actuallyscans the surface. Therefore, in order that the curve as a whole maybecome closer to the ideal scan line, the amount of screwing for thescrews for adjustment 37 to 39 is adjusted. The rotating operation ofthe screws for adjustment at this time is performed, for example, asfollows:

[0078] (1) Parallel movement in the upward and downward direction (thedirection of sub-scanning)

[0079] All the screws for adjustment 37 to 39 are rotated in the samedirection.

[0080] (2) Tilting movement in the upward and downward direction(Rotation around an axis parallel to the main scanning direction)

[0081] The screws for adjustment 37 and 38 are rotated in the samedirection, or the screw for adjustment 39 is rotated.

[0082] (3) Tilting movement in the left and right direction (Rotationaround an axis perpendicular to the surface to be scanned)

[0083] The screw for adjustment 37 or 38 is rotated.

[0084] (4) Correction (for example, correction for bending)

[0085] This is possible in the case where the second cylindrical lens 6is capable of bending like a plastic lens; the screws for adjustment 37to 39 are independently rotated.

[0086] In addition, this invention concerning a scanning optical deviceis not limited to the above-mentioned example of the embodiment. Forexample, it is possible for the scanning optical device to have astructure as follows:

[0087] (A) The contact member is not limited to a screw for adjustment,and the number of the contact members is not limited to three. If thenumber of the contact members is increased, generally speaking, therange of adjustment such as correction is broadened, and also theprecision of adjustment is improved.

[0088] (B) It is not required that all of the contact members arecapable of moving in the upward and downward direction. For example, ina structure wherein the screws for adjustment 36 and 37 in theabove-mentioned example of the embodiment is not capable of moving, theprojections 19 and 20 are used as the contact members at this portionand the screws for adjustment 36 and 37 are not provided.

[0089] (C) The urging means is not limited to a leaf spring, and thenumber is not limited to two. In a structure wherein an elastic membersuch as a rubber is pressed, it is possible that the whole upper surfaceof the second cylindrical lens 6 is pressed by the elastic member.

[0090] (D) If it is desired that play for the screws for adjustment 37to 39 in the axial direction against the base 1 is eliminated, it may beappropriate to make a structure such that a coil spring or the like isdisposed between the head portion of the screws 37 to 39 and the base 1,in order that the screws for adjustment 37 to 39 may be always urged tothe downward direction.

[0091] (E) The fixing of the optical parts such as the secondcylindrical lens 6 is not limited to adhesive bonding.

[0092] (F) Although the correction for the scan lines is done by onlythe second cylindrical lens 6 in the above-mentioned example of theembodiment, it is possible to provide a mechanism for adjusting anddetermining the position in both of the second cylindrical lens 6 andthe fθ lens 5 respectively.

[0093] (G) It is also possible to carry out the adjustment anddetermination of the position of the second cylindrical lens 6automatically. In this case, as a matter of course, the signal from thesensor on the surface to be scanned is fed back to the control portion,and the amount of screwing of the screws for adjustment 37 to 39 isadjusted by the control portion in order that actual scan lines maybecome closer to the ideal scan line.

THE SECOND EXAMPLE OF THE EMBODIMENT

[0094]FIG. 9 is a drawing showing the structure of an example of theembodiment of this invention concerning an image forming apparatus. Inan image forming apparatus in this example of the embodiment, formationof a color image using toners of four colors Y, M, C, and K with fourscanning optical devices arranged in the direction of sub-scanning.

[0095] In FIG. 9, the belt-shaped image bearing member 100 is driven inthe clockwise direction (direction of the arrow marks), being entrainedaround the rollers 101 to 109. In the neighborhood of the image bearingmember 100, there are arranged the scanning optical devices 111 to 114in the direction of sub-scanning in such a manner as to face toward theimage bearing member 100. Each of the scanning optical devices 111 to114 has the same structure as has been shown in the above-describedfirst example of the embodiment, that is, the structure comprising atleast a light source, a collimator lens into which a light beam havingbeen emitted from said light source enters, a deflector which deflectsthe light beam having passed said collimator lens to the direction ofmain scanning, and an image forming lens which focuses the light beamhaving passed said deflector on the surface to be scanned of the imagebearing member.

[0096] In the above, the scanning optical device 111 is one for forminga latent image for Y (yellow) by using a laser beam, the scanningoptical device 112 is one for forming a latent image for M (magenta) byusing a laser beam, the scanning optical device 113 is one for forming alatent image for C (cyan) by using a laser beam, and the scanningoptical device 113 is one for forming a latent image for K (black) byusing a laser beam.

[0097] Each of the scanning optical devices 111 to 114 is linked to theneighboring devices after determining the position. This linking is doneby using a link member. To describe it concretely, as shown in FIG. 10,the link member 200 is fixed to the both side portions of the respectivescanning optical devices 111 to 114 by using the plural screws 201 in amanner capable of being taken off, and after that, as shown in FIG. 11,the position of the one of the neighboring scanning optical devices isdetermined in the state of floating off against the other, and then theupper end surface and the lower end surface of the respective linkmembers of the neighboring scanning optical devices are bonded to eachother by using an adhesive of the UV-setting type or the like.

[0098] In this example of the embodiment, it is used the structurewherein the scanning optical devices 113 to 111 is successively stackedon the scanning optical device 114 one after another. In addition,although the link member 200 and the screws 201 is not necessary in thefirst example of the embodiment, they are shown in FIG. 1 to FIG. 3 forthe purpose of making it easy to understand the structure of linking ofthe scanning optical devices in the second example of the embodiment.

[0099] In FIG. 9 again, at the respective front stages of the scanningoptical devices 111, 112, 113, and 114, the charging portions 121, 122,123, and 124, which give the image bearing member 100 electrostaticcharges for Y, M, C, and K respectively, are provided; at the respectiverear stages of the scanning optical devices 111, 112, 113, and 114,there are provided the developing units 131, 132, 133, and 134, whichdevelop the latent images formed by the respective scanning opticaldevices 111, 112, 113, and 114 by using the developers for Y, M, C, andK respectively.

[0100] The transfer paper 142 in the paper feeding portion 141 isconveyed out by the paper feeding roller 143, and is fed to the transferportion 151 by the transport roller pair 144 and the timing roller 145.This transfer portion 151 is composed of the transfer electrode 152which transfers the toner image on the image bearing member 100 to thetransfer paper 142 by corona discharging, and the pick off electrode 153which picks off the transfer paper 142 from the image bearing member 100by alternate current discharging.

[0101] The fixing portion 161 is composed of the heat roller 162 and thepressing roller 163, and fuses the toner image to stick to the transferpaper. The transfer paper 142 after this fixing process is ejected ontoa receiving tray by the transport portion 171 at the rear stage of thefixing portion 161. Further, the residual toner particles remaining onthe image bearing member 100 after transfer are scraped off in thecleaning portion 191, and are received in the collecting box 192.

[0102] In this example of the embodiment, the scanning optical devices111 to 114 and the developing units 131 to 134, which are assigned tothe colors Y, M, C, and K respectively, are arranged for every color inthe direction of sub-scanning; the scanning optical devices for therespective colors 111 to 114 are let to form the latent electrostaticimages for the respective colors in a manner such that all the colortoner images should be mutually superposed precisely, and the developingunits 131 to 134 are let to develop the latent images respectively. Thatis, after forming the toner image of Y by using the scanning opticaldevice Ill and the developing unit 131, the toner image of M is formedon the toner image of Y superposed by using the scanning optical device112 and the developing unit 132, and the toner image of C is formed onthem by using the scanning optical device 113 and the developing unit133, and lastly the toner image of K is formed superposed on them byusing the scanning optical device 114 and the developing unit 134; thesesteps complete the formation of color toner image, which is transferredto the transfer paper 142 at the transfer portion 151.

[0103] In the case where independent scanning optical devices are usedfor the respective colors as described in the above, it is necessarythat each of the scanning optical devices forms a latent image in amanner such that it is precisely superposed on the others. In otherwords, it is necessary to let the respective scanning optical devices111 to 114 trace scan lines of the same characteristic (the firstcondition), and also it is necessary to determine the positions of therespective scanning optical devices 111 to 114 in order that the scanlines traced by the respective scanning optical devices are superposedon one another (the second condition).

[0104] In this example of the embodiment, as for the scanning opticaldevices 111 to 114, the scanning optical device shown in FIG. 1 to FIG.3 (the first example of the embodiment) is employed; therefore, it iseasy to adjust each of the scanning optical devices 111 to 114 in orderthat they may trace scan lines having the same characteristic, and thefirst condition can be satisfied. Especially, if the optical parts forthe second cylindrical lens etc designed to be of the same shape andmaterial and obtained from the same manufacturing lot are used, thecharacteristics of the optical parts as the individual ones are made tobe the same; thus, because the only thing to do further is merely toadjust and determine the positions of the optical parts, it is easier tolet each of the scanning optical devices 111 to 114 trace scan lines ofthe same characteristic.

[0105] On the other hand, in order to satisfy the second condition, inthis example of the embodiment, for the scanning optical devices 111 to114 of which the adjustment of the individual device has been completedand of which to the both side portions the link members 200 are fixedrespectively by using the plural screws 201 for each in a manner capableof being taken off, the positions are determined with one of theneighboring scanning optical devices let to be in the state of floatingoff against the other, and the upper end surface and the lower endsurface of the respective link members of the neighboring scanningoptical devices are bonded to each other by using an adhesive of theUV-setting type or the like.

[0106] As for the fixture for adjustment, in this example, it is used afixture that is equivalent to one made up of four fixtures stacked onone another with a predetermined spacing, each of them being used at thetime of adjustment for the first example of the embodiment. That is, itis used a fixture wherein four parallel ideal scan lines correspondingto the colors Y, M, C, and K respectively are assumed to be on thesurface to be scanned, and a plurality of sensors are disposed on eachof the ideal scan lines. Each of the sensors can detect to what degreean actual beam is deviated from the above-mentioned ideal scan line.

[0107] The operation of adjustment is carried out as follows. First, abeam is generated in the scanning optical device 114, and the positionof this is determined in order that the actual scan line by this beam issuperposed on the ideal scan line for the color K (the scanning opticaldevice 114 is attached to the fixture for adjustment).

[0108] Next, the scanning optical device 113 is supported in the stateof floating off against the scanning optical device 114, and is let togenerate a beam; the position is determined in order that the actualscan line of the beam may be superposed on the ideal scan line for thecolor C, and the upper end surface and the lower end surface of therespective link members 200 of the scanning optical devices 114 and 113are bonded to each other by an adhesive of the UV-setting type.

[0109] Further, the scanning optical device 112 is supported in thestate of floating off against the scanning optical device 113, and islet to generate a beam; the position is determined in order that theactual scan line of the beam may be superposed on the ideal scan linefor the color M, and the upper end surface and the lower end surface ofthe respective link members 200 of the scanning optical devices 113 and112 are bonded to each other by an adhesive of the UV-setting type.

[0110] Lastly, the scanning optical device 111 is supported in the stateof floating off against the scanning optical device 112, and in the sameway, the position is determined in order that the actual scan line ofthe beam may be superposed on the ideal scan line for the color Y, andthe upper end surface and the lower end surface of the respective linkmembers 200 of the scanning optical devices 112 and 111 are bonded toeach other by an adhesive of the UV-setting type.

[0111] In this connection, as for the cause of the relative deviation ofthe positions between the neighboring scanning optical devices, thefollowing will be cited:

[0112] (1) Deviation in the upward and downward direction with regard tothe surface to be scanned (in the direction of sub-scanning)

[0113] The scan lines also deviate in the upward and downward direction.

[0114] (2) Deviation in the left and right direction with regard to thesurface to be scanned (in the direction of main scanning)

[0115] The scan lines also deviate in the left and right direction.

[0116] (3) Deviation in the direction perpendicular to the surface to bescanned

[0117] The length of the scan line is increased or decreased (lateralmagnification is varied).

[0118] (4) Tilt around a horizontal axis perpendicular to the surface tobe scanned

[0119] The scan lines are tilted in the upward and downward direction.

[0120] (5) Rotation around an vertical axis parallel to the surface tobe scanned

[0121] The pixel density (interval between the neighboring pixels) onthe scan lines is made large at one end portion and is made small at theother end portion.

[0122] The detection of the above-described (1) to (5) can be done bydisposing three sensors on the ideal scan line. For example, if threesensors which detect respectively the position of the beam spot at thestarting point, at the ending point, and at the center of the beam to betraced actually by the scanning optical device, the deviations (1) to(4) can be easily detected from the position of the beam spot at thestarting point and the ending point, and the deviation (5) can bedetected by judging to which side the beam spot at the center shifts,the starting point or the ending point.

[0123] In this example of the embodiment, because the scanning opticaldevice to be determined for its position is supported in a state offloating off against the neighboring scanning optical device with an armof an assembling robot or the like for carrying out the adjustment, thescanning optical device can be shifted in any direction. Therefore, theabove-described deviations of the position can be easily reduced on thebasis of the outputs of the plural sensors. Further, it is determinedhow high the precision of the adjustment and determination of theposition by to what degree the image quality is required for the imageforming apparatus.

[0124] By an experiment of the inventors, it has been confirmed that ifthe deviation of the latent images for the colors Y, M, C, and K formedon the surface to be scanned is not larger than 200 μm, or desirably notlarger than 120 μm, the image can be recognized as an image giving nofeeling of disorder.

[0125] It is possible to carry out the above-described linking of thescanning optical devices in the state of being loaded in the imageforming apparatus, however actually, it makes the operation far moresimple to link the plural scanning optical devices beforehand and thenload the image forming apparatus with the scanning optical devices inthe linked state.

[0126] As is obvious from the foregoing explanation, in this example ofthe embodiment, the positions of the plural scanning optical devices 111to 114 to be arranged in the direction of sub-scanning are adjusted anddetermined with the devices made to be in the state of floating, and thelink members are mutually linked after the determination of thepositions. Owing to this, by once precisely adjusting and determiningthe positions of the scanning optical devices 111 to 114, the positionalrelationship among the scanning optical devices 111 to 114 will never bevaried after that, and the deterioration of image quality owing to thescanning optical devices 111 to 114 can be prevented.

[0127] Further, because the link members 200 are fixed to the scanningoptical devices 111 to 114 in a manner capable of being taken off, inthe case where the determination of the positions is proved to be notsatisfactory after the linking of the neighboring scanning opticaldevices, it is possible that the link members 200 are taken off from thescanning optical devices 111 to 114, with the state of mutual linking ofthe link members 200 let to remain as it is, and then, new link members200 are attached to the scanning optical devices 111 to 114, and thepositions are determined again, and the new link members 200 are fixedto one another. Owing to this, it has become possible to utilize againthe scanning optical devices 111 to 114.

[0128] Furthermore, because an adhesive of the UV-setting type is usedfor fixing the link members 200 to one another, it is possible that thedetermination of the positions is carried out with a suitable amount ofthe adhesive injected between the link members, and the fixing isperformed immediately after determining the positions by applying anultra-violet ray; hence, the inking operation is made easy.

[0129] Besides, the above-described method of linking of the scanningoptical devices 111 to 114 is one wherein the scanning optical devices111 to 114 are successively linked one by one; however, it is possibleto bond these devices at the same time after the positions of all thescanning optical devices 111 to 114 are determined. Further, in theabove-described example of the embodiment, the link members 200 arefixed to one another by an adhesive of the UV-setting type; however, asa matter of course, it is possible to use other types of adhesive, andalso it is possible to screw the link members or to weld them.Furthermore, because the deviation of the latent images for the colorsY, M, C, and K can be detected by utilizing the technology of what iscalled pattern recognition, it may be appropriate to detect thedeviation of the positions by this method.

[0130] In some cases, keeping the superposition of the scan lines surecan be performed not only by the hardware-like method of adjusting anddetermining the positional relationship among the scanning opticaldevices 111 to 114, but also by a software-like adjustment method todevise how to drive the scanning optical devices. However, because itincreases the burden on the software, it is desirable to make adjustmentby a hardware-like method as far as possible.

[0131] As has been explained in the foregoing, in this inventionconcerning a scanning optical device, it is provided a mechanism foradjusting and determining the position of the image forming lenscomprising contact members capable of being in contact with the imageforming lens respectively at the three points, that is, the both endportions of the image forming lens in the main scanning direction and anintermediate portion between these both end portions and an urging meansfor urging the image forming lens to the contact members. The imageforming lens is positioned in the vicinity of the surface to be scanned,and is easy to be subjected to bending owing to its long size. In spiteof this, according to this invention for adjusting the position offixing this image forming lens, the scanning beam is corrected easilyand with a good efficiency. In addition to it, because the image forminglens is in contact with the contact members at the three points, namely,the both end portions in the main scanning direction and an intermediateportion between the both end portions respectively at the time ofadjusting the position of the image forming lens, it is possible to letthe image forming lens take any position by displacing the points ofcontact.

[0132] In the above-described invention, the points of contact of theimage forming lens at its both end portions in the main scanningdirection with the contact member are positioned on a straight linewhich is approximately parallel to the main scanning direction, and thepoint of contact at the intermediate portion is placed at a positiondeviated from a position on the above-mentioned straight line in thedirection perpendicular to the surface to be scanned. Owing to this, theadjustment of position of the image forming lens can be performed bymoving at least one of the contact members placed at the above-mentionedthree points of contact in the direction of sub-scanning.

[0133] It is desirable that the image forming lens is fixed to the basein order to prevent the deviation of the position of the image forminglens after the adjustment of the position of the image forming lens. Inthe above-described invention, this fixing is made at a position in theneighborhood of the point of contact at the intermediate portion of theimage forming lens. Owing to this, the image forming lens is fixed onlyat the intermediate portion, which makes it possible for the imageforming lens to expand and contract freely in accordance with thevariation of temperature and humidity of the surrounding; thus the imageforming lens is never bent unnaturally and it can be avoided theunfavorable influence that a complex bending etc are produced in thescan lines.

[0134] According to this invention concerning an image formingapparatus, the positions of a plurality of scanning optical devicesarranged in the direction of sub-scanning are adjusted and determined inthe state of floating off against the others, and the linking membersare mutually linked after determining the positions. Owing to this, byonce precisely adjusting and determining the positions of the scanningoptical devices, the positional relationship among the scanning opticaldevices will never be varied after that, and the deterioration of imagequality owing to the scanning optical devices can be prevented.

[0135] Further, because the linking members are fixed to the respectivescanning optical devices in a manner capable of being taken off, in thecase where the determination of the positions is proved to be notsatisfactory after the linking of the neighboring scanning opticaldevices, it is possible that these link members are taken off from thescanning optical devices, with the state of mutual linking of the linkmembers let to remain as it is, and then new link members are attachedto the scanning optical devices, and the positions are determined again,and the new link members are fixed to one another. Owing to this, it hasbecome possible to utilize again the scanning optical devices.

[0136] In this invention concerning an image forming apparatus, as ascanning optical device, the above-described one is used, and at thesame time, the mutual linking of the neighboring optical devices is madein the same manner as described in the above-described invention. Owingto this, according to this invention, in the respective scanning opticaldevices, the scanning beam can be corrected easily and with a goodefficiency. Further, because the linking members are mutually linkedafter determining the positions, the positional relationship among thescanning optical devices is never varied, and the deterioration of imagequality owing to the scanning optical device can be prevented.Furthermore, reutilization of the scanning optical devices has becomepossible.

[0137] Because an adhesive of the UV-setting type is used for fixing theabove-described link members to one another, fixing can be madeimmediately after determining the positions, and the linking operationis made easy.

What is claimed is:
 1. A scanning optical system, comprising: a plurality of scanning optical devices, each scanning optical device including a light source to emit a light beam, a collimator lens into which the light beam emitted from the light source enters, a deflector to deflect the light beam passing through the collimator lens in a main scanning direction, an image forming lens to focus the light beam coming from the deflector onto a scanned surface, and a base plate on which the light source, the collimator lens, the deflector and the image forming lens are fixed, wherein the plurality of scanning optical devices are piled up in a sub-scanning direction perpendicular to the main scanning direction in such a manner that each base plate is substantially parallel to other base plates; and a plurality of link members to connect two neighboring base plates independently of other base plates.
 2. The scanning optical system of claim 1 , wherein each of the plurality of link member is removably fixed to one of the base plates, and the link member fixed to one of the two neighboring base plates is fixed to the link member fixed to the other one of the two neighboring base plates after a position of the one of the two neighboring base plates is adjusted in relation to a position of the other one of the two neighboring base plates.
 3. The scanning optical system of claim 2 , wherein the link member are fixed with adhesive hardenable with ultraviolet rays.
 4. A scanning optical system, comprising: a plurality of scanning optical devices, each scanning optical device including a light source to emit a light beam, a collimator lens into which the light beam emitted from the light source enters, a deflector to deflect the light beam passing through the collimator lens in a main scanning direction, an image forming lens to focus the light beam coming from the deflector onto a scanned surface, a contact member to come in contact with a first side surface of the image forming lens at three contact points on both end portions and a middle portion of the first side surface in terms of the main scanning direction; a pressing member to come in pressure contact with a second side surface of the image forming lens so as to press the image forming lens toward the contact member and a base plate on which the light source, the collimator lens, the deflector, the image forming lens, the contact member and the pressing member are fixed, wherein the plurality of scanning optical devices are piled up in a sub-scanning direction perpendicular to the main scanning direction in such a manner that each base plate is substantially parallel to other base plates; and a plurality of link members to connect two neighboring base plates independently of other base plates.
 5. The scanning optical system of claim 4 , wherein the contact member comprises three contactors provided separately to come in contact with the first side surface at the three contact points, and each of the three contactors is adapted to move independently of the other pieces so that positioning for the image forming lens is conducted by moving the three contactors separately.
 6. The scanning optical system of claim 4 , wherein each of the plurality of link member is removably fixed to one of the base plates, and the link member fixed to one of the two neighboring base plates is fixed to the link member fixed to the other one of the two neighboring base plates after a position of the one of the two neighboring base plates is adjusted in relation to a position of the other one of the two neighboring base plates.
 7. The scanning optical system of claim 4 , wherein the link member are fixed with adhesive hardenable with ultraviolet rays.
 8. A scanning optical device, comprising: a light source to emit a light beam; a collimator lens into which the light beam emitted from the light source enters; a deflector to deflect the light beam passing through the collimator lens in a main scanning direction; an image forming lens to focus the light beam coming from the deflector onto a scanned surface; a contact member to come in contact with a first side surface of the image forming lens at three contact points on both end portions and a middle portion of the first side surface in terms of the main scanning direction; and a pressing member to come in pressure contact with a second side surface of the image forming lens so as to press the image forming lens toward the contact member.
 9. The scanning optical device of claim 8 , wherein the contact member comprises three contactors provided separately to come in contact with the first side surface at the three contact points, and each of the three contactors is adapted to move independently of the other pieces so that positioning for the image forming lens is conducted by moving the three contactors separately.
 10. The scanning optical device of claim 9 , wherein two contact points on the both end portions are arranged such that a line connecting the two contact points is parallel to the main scanning direction and the contact point on the middle portion is deviated from the line, and wherein at least one of the three contactors shifts the image forming lens in a sub-scanning direction perpendicular to the main scanning direction.
 11. The scanning optical device of claim 9 , wherein the tree contactors are fixed after the positioning. 